JP2975652B2 - Receiving frequency measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reception frequency measuring device capable of receiving a frequency quickly and accurately and analyzing its frequency component.

[Conventional technology]

The receiving frequency measurement device uses an AFC that stabilizes the frequency of the local oscillation signal using the DC component of the demodulated signal from the frequency discriminator.
A circuit is provided.

The AFC circuit controls the frequency of the local oscillation signal based on the output from the frequency discriminator so that the input signal comes to the center of the selected bandwidth, and detects the frequency of the input signal.

When the selection bandwidth of the frequency of the input signal is narrow, for example, 50 KHz or less, a crystal can be used for the frequency discriminator, and as a result, the temperature drift characteristics can be highly stabilized.

However, in the radio wave monitoring device, for the purpose of monitoring illegal radio waves, the selection bandwidth of the frequency of the input signal is, for example,
A broadband of about 1 MHz is required. Since a crystal with a narrow bandwidth cannot be used for such a broadband frequency discriminator, a frequency discriminator including a resistor and a capacitor (hereinafter, referred to as RC) is used.

However, the frequency drift characteristics of RC frequency discriminators are not good. Therefore, for example, even if the output voltage of the frequency discriminator is adjusted to be 0 V at the center frequency of the selected band, the output voltage changes due to a change in temperature, causing a shift in the center frequency. The output frequency is measured incorrectly.

Therefore, AF that does not depend on the temperature drift of the frequency discriminator
A device for the C circuit is disclosed (see Japanese Utility Model Publication No. 59-34198). To explain the outline of the invention, first, a signal of a reference frequency is input to a frequency discriminator for a specific period. Next, the output of the frequency discriminator at that time, that is, the output error voltage due to the temperature drift is stored. Then, when configuring the AFC loop, the error due to the temperature drift is removed by controlling the voltage controlled oscillator based on the difference between the output of the frequency discriminator and the previously stored voltage.

[Problems to be solved by the invention]

However, the AFC circuit of the present invention still has a problem.

That is, in the AFC circuit, the problem inherent in the AFC circuit that it takes a certain time to pull in the frequency of the local oscillation signal has not been solved at all.

 Hereinafter, this problem will be described.

In the AFC circuit, the DC component voltage of the demodulated signal from the frequency discriminator is compared with a reference voltage (for example, 0 V when the input frequency of the frequency discriminator (hereinafter, referred to as an intermediate frequency) is fIF) by the comparator 10. In comparison, when the DC component voltage is higher than the reference voltage, the voltage f L0 is corrected in the direction of decreasing the voltage, and when the DC component voltage is lower than the reference voltage, the voltage is increased in the direction of increasing the voltage. Operation is required, and correction is performed so that the DC component voltage matches the reference voltage.

As a result, the frequency fR of the target input signal is changed from fL0 after correction to f
It is obtained by subtracting IF, that is, fR = f L0−f IF.

However, the time required for correction (for example, lock-up time in the case of a local oscillator) is naturally necessary,
This time cannot be lost.

[Means for solving the problem]

In order to solve the above problems, the present invention employs the following solutions.

 The configuration of the apparatus of the present invention will be described with reference to FIG.

The local signal oscillator 1 oscillates a local signal f L0 for the frequency fR of the input signal.

The mixer 2 mixes the frequency fR of the input signal with the frequency fL0 of the local signal from the local signal oscillator 1 to generate an intermediate frequency signal fIF.

Oscillator 3 oscillates a reference frequency to frequency discriminator 5.

The switch 4 switches between a signal from the mixer 2 and a signal from the oscillator 3.

The frequency discriminator 5 converts the intermediate frequency fIF or the reference frequency into a voltage V.

The A / D converter 6 converts the output voltage of the frequency discriminator 5 from an analog signal to a digital signal.

The memory 7 stores digital data whose reference frequency has been converted to voltage.

The calculation unit 8 calculates the frequency fR of the input signal based on the characteristics of the frequency discriminator 5 checked based on the reference frequency stored in the memory 7, the voltage V of the intermediate frequency fIF, and the local frequency fL0.

 The control unit 9 controls the memory 7 and the arithmetic unit 8.

 The operation of the device of the present invention will be described in detail below.

The switch 4 is selected on the oscillator 3 side and the two reference frequencies f
By inputting f1 and f2, the frequencies f1 and f2 are converted from the frequencies into voltages V1 and V2, and the frequency versus output characteristic of the frequency discriminator 5 is obtained.

Next, the voltages V1 and V2 are stored in the memory 7, respectively.

Next, the switch 4 is selected on the mixer 2 side, and the output voltage V of the frequency discriminator and the frequencies f1, f2 and V1, V2 are substituted into the following equation.

Then, as a result of calculating the equation, the intermediate frequency fIF is found.

In the device of the present invention, since the frequency of the local oscillator is fixed with respect to the input signal, fR = f L0 can be obtained without requiring the time for pulling in the frequency of the local oscillator such as an AFC circuit.
The frequency of the input signal fR can be determined from −f IF.

Further, in this device, even when a temperature drift occurs in the frequency discriminator 5, a straight line of the frequency versus output characteristic is determined from the two reference frequencies f1 and 2f.
Is found.

〔Example〕

 The configuration of the present invention will be described with reference to FIG.

A local signal oscillator 1 and a mixer 2 for frequency-converting an input signal by the local signal
An oscillator 3 for generating two reference frequencies, a switch 4 for selecting and switching between the output of the mixer 2 and the output of the oscillator 3, a frequency discriminator 5 for converting the output from the switch 4 into a frequency and a voltage, An A / D converter 6 for converting the output from the frequency discriminator 5 from analog to digital, and outputs V1 and V2 of the A / D converter 6 corresponding to the first reference frequency 1f and the second reference frequency f2, respectively. The memory 7 to be stored, and the outputs V1 and V2 of the A / D converter 6 are stored in the memory 7, and the switch 4 is selectively switched to the oscillator 3 side to check the characteristics of the frequency discriminator 5 and A control unit 9 for storing the outputs of the A / D converters; and a frequency versus output characteristic of the frequency discriminator 5 is calculated based on the output from the memory 7, and the selector and the switch 4 are selectively switched to the input signal side. The output V from the A / D converter 6 at that time and the frequency of the local signal A calculation unit 8 for calculating the frequency fR of the input signal from the wave number f L0.

Next, the procedure for obtaining the frequency of the input signal according to the present invention will be described in the first step.
This will be described with reference to FIGS.

First, the switch 4 is switched to the oscillator 3 that oscillates the reference frequencies f1 and f2.

The reference frequencies f1 and f2 are converted by the frequency discriminator 5 into corresponding voltages V1 and V2, respectively.

After converting the voltages V1 and V2 from analog signals to digital signals, each is stored in a memory.

The switching unit 4 is switched to the mixer 2 side to convert the frequency fR of the input signal into a frequency and input to the frequency discriminator 5.

The frequency discriminator 5 converts the frequency into a voltage,
The voltage V is substituted into the following equation.

By calculating the above equation, an intermediate frequency fIF is obtained.

After that, the frequency of the input signal fR is obtained by performing an operation of fR = fL0-fIF from the intermediate frequency fIF and a predetermined frequency fL0 of the local signal.

Even if the temperature drift of the frequency discriminator 5 occurs,
By determining the corresponding voltages V1T and V2T from the reference frequencies f1 and f2, the frequency versus output characteristics can be determined, and thereby the frequency of the input signal can be determined (see FIG. 2).

As another embodiment, a superheterodyne system in which the mixer 2 has a plurality of stages is naturally effective.

Further, by switching the frequency of the local signal oscillator 1 in a stepwise manner for each selected band, a receiver capable of coping with a wide band stores an illegal radio wave detected in a certain band, continues scanning, and later scans the illegal radio wave. It is also possible to check the radio waves.

In the embodiment of the present invention, the calculation is performed by the calculation unit 8. However, the frequency of the input signal can be obtained by storing a table in the memory and substituting the voltage value of the input signal there. Becomes

Further, in the embodiment of the present invention, two reference signals are input and their frequency-voltage characteristics are calculated. However, if the frequency-voltage characteristics of the frequency discriminator 5 are not linear, three or more points are measured. It is naturally conceivable to do so.

〔The invention's effect〕

First, it has become possible to quickly and accurately detect the frequency of an input signal. As a result, it is effective in detecting illegal radio waves in which radio waves disappear instantaneously.

Next, since the output from the frequency discriminator is A / D converted, it can be processed by the CPU as digital data.

Further, even a frequency discriminator using a crystal is not completely free from temperature drift, and if this method is used, a more accurate measurement of the reception frequency can be performed.

[Brief description of the drawings]

 FIG. 1 is a diagram showing the configuration of the device of the present invention, FIG. 2 is a diagram showing the characteristics of the frequency discriminator of the present invention, and FIG. 3 is a diagram showing the configuration of a conventional AFC circuit. 1 ... local signal oscillator, 2 ... mixer, 3 ... oscillator, 4 ... switcher, 5 ... frequency discriminator, 6 ... A / D converter, 7 ... memory, 8 ... arithmetic unit, 9 ... control unit, 10 ... comparator.

Claims (1)

(57) [Claims] 1. A local signal oscillator, a mixer for converting a frequency of an input signal by a local signal, an oscillator for generating at least two first and second reference frequencies, and an output of the mixer and an output of the oscillator. A switch for performing selection switching,
A frequency discriminator for converting the output from the switch into a frequency voltage, an A / D converter for converting an analog signal output from the frequency discriminator into a digital signal, the first reference frequency and the second reference A memory for storing an output of the A / D converter corresponding to a frequency, a control unit for storing an output of the A / D converter when the switch is selectively switched to the oscillator side, and the memory, Calculates the frequency versus output characteristic of the frequency discriminator according to the output from the A / D converter and the output of the A / D converter when the selector is selectively switched to the mixer side and the input from the frequency of the local signal. A receiving frequency measuring device comprising: a calculating unit that calculates a frequency of a signal.